Technical Field
The present invention relates to a semiconductor device producing method in which dopants implanted into a semiconductor substrate are activated by the irradiation with a laser beam.
Related Art
Japanese Unexamined Patent Application Publication No. 2010-171057 (PTL1) discloses a semiconductor device producing method in which an electrode layer and a field stop layer are formed by introducing dopants into a semiconductor substrate by ion implantation and then activating the dopants by the irradiation with a laser beam. In the technique described in PTL 1, after a surface structure of a semiconductor device is fabricated, the substrate is thinned. Thereafter, ion implantation is performed on a rear surface and the rear surface is irradiated with pulsed laser beams by using two laser oscillators. A temporal difference between laser pulses which are emitted from the two laser oscillators is set to be less than or equal to 600 ns.
Specifically, for example, phosphorus ions are ion-implanted into a field stop layer formation planned portion from the rear surface side of an n− type silicon substrate. At this time, a dose amount is set to be less than or equal to 1×1014 cm−2 such that the field stop layer has peak concentration of less than or equal to 5×1018 cm−3. Subsequently, for example, boron ions and phosphorus ions are respectively implanted into a p+ type collector layer formation planned portion and an n+ type cathode layer formation planned portion with a dose amount set to be less than or equal to 5×1016 cm−2 such that the a p+ type collector layer and an n+ type cathode layer have peak concentration of less than or equal to 1×1021 cm−3.
It is known that the n+ type cathode layer or the like in which ions are implanted at such high concentration is amorphized due to breaking of the crystallinity of the silicon substrate. In the semiconductor device producing method described in PTL 1, defect recovery by solid-phase diffusion and the activation of the dopants implanted into a deep portion exceeding a depth of 1 μm from a laser irradiated surface (the rear surface of the substrate) are performed using the laser irradiation. However, sufficient temperature rise and heating time cannot be secured, and thus the activation of the dopants may be insufficient. If the pulse energy density of the laser beam which is input is increased in order to sufficiently perform the activation of the deep portion, a melting depth becomes deep. If melting is made to the deep portion, dopant concentration distribution in a depth direction changes, and thus characteristics as designed cannot be obtained in some cases. In addition, a problem occurs such as the roughness of the substrate surface becoming worse.
A technique of performing laser annealing by emitting a pulsed laser beam at a pulse energy density in the range in which a semiconductor substrate is not melted is proposed (refer to Japanese Unexamined Patent Application Publication No. 2009-32858, for example). In this method, dopants are ion-implanted at high concentration, and thus it is difficult to sufficiently recover the crystallinity of an amorphized portion and sufficiently activate the implanted dopants.